As is known, the bleeding time in vitro can be measured since according to FIG. 15, blood 9' can be sucked from a supply vessel 7' via an aperture 5' into a cylinder 6', inasmuch as in the cylinder 6', a plunger 3' is moved by a stepping motor 2' in the direction of the arrow 11'. A pressure sensor 4' thereby measures the pressure prevailing in the chamber precircuited to plunger 3'. This pressure will be held to a constant value such that a processor 1' drives the stepping motor 2' as a function of the signal of the pressure sensor 4'. From the movement of the plunger 3' and the diameter of the cylinder 6', the processor 1' computes the volume flow of the blood through the aperture 5'. The aperture 5', whose diameter is at about 150 .mu.m for example, simulates an injured portion of an arteriole. It is located for instance, in a cellulose acetate filter that is coated with collagen. The filter will be saturated with ADP before the measurement. According to the described method, a reproducible measurement of the bleeding time in vitro and of the bleeding volume is possible.
As is known, the aperture 5', that is, the stated filter, is positioned in a housing 10' that can be joined to a capillary 8' that sucks the blood 9' taken from the supply vessel 7' to the aperture 5'.
Now in the described measurement method, one problem consists in the fact that when carrying out a large number of measurements, for example, about 150 measurements per day, a correspondingly large number of aperture holders 10' is needed. These aperture holders 10' that contain the described collagen-coated filters as apertures 5', must be stored in a refrigerator or similar appliance at about 4.degree. C. until they are used. This means that when carrying out measurements on a large scale, the available cooling space needed to prepare the aperture holder 10' will have to be quite large.
The problem of the present invention consists in designing a device for the automatic examination of blood samples where relatively many aperture holders can be positioned in a comparatively small space.